1 /* SPDX-License-Identifier: GPL-2.0+ */ 2 /* 3 * Read-Copy Update mechanism for mutual exclusion 4 * 5 * Copyright IBM Corporation, 2001 6 * 7 * Author: Dipankar Sarma <[email protected]> 8 * 9 * Based on the original work by Paul McKenney <[email protected]> 10 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. 11 * Papers: 12 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf 13 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) 14 * 15 * For detailed explanation of Read-Copy Update mechanism see - 16 * http://lse.sourceforge.net/locking/rcupdate.html 17 * 18 */ 19 20 #ifndef __LINUX_RCUPDATE_H 21 #define __LINUX_RCUPDATE_H 22 23 #include <linux/types.h> 24 #include <linux/compiler.h> 25 #include <linux/atomic.h> 26 #include <linux/irqflags.h> 27 #include <linux/preempt.h> 28 #include <linux/bottom_half.h> 29 #include <linux/lockdep.h> 30 #include <asm/processor.h> 31 #include <linux/cpumask.h> 32 #include <linux/context_tracking_irq.h> 33 34 #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) 35 #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) 36 #define ulong2long(a) (*(long *)(&(a))) 37 #define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b))) 38 #define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b))) 39 40 /* Exported common interfaces */ 41 void call_rcu(struct rcu_head *head, rcu_callback_t func); 42 void rcu_barrier_tasks(void); 43 void rcu_barrier_tasks_rude(void); 44 void synchronize_rcu(void); 45 46 struct rcu_gp_oldstate; 47 unsigned long get_completed_synchronize_rcu(void); 48 void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp); 49 50 // Maximum number of unsigned long values corresponding to 51 // not-yet-completed RCU grace periods. 52 #define NUM_ACTIVE_RCU_POLL_OLDSTATE 2 53 54 /** 55 * same_state_synchronize_rcu - Are two old-state values identical? 56 * @oldstate1: First old-state value. 57 * @oldstate2: Second old-state value. 58 * 59 * The two old-state values must have been obtained from either 60 * get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or 61 * get_completed_synchronize_rcu(). Returns @true if the two values are 62 * identical and @false otherwise. This allows structures whose lifetimes 63 * are tracked by old-state values to push these values to a list header, 64 * allowing those structures to be slightly smaller. 65 */ 66 static inline bool same_state_synchronize_rcu(unsigned long oldstate1, unsigned long oldstate2) 67 { 68 return oldstate1 == oldstate2; 69 } 70 71 #ifdef CONFIG_PREEMPT_RCU 72 73 void __rcu_read_lock(void); 74 void __rcu_read_unlock(void); 75 76 /* 77 * Defined as a macro as it is a very low level header included from 78 * areas that don't even know about current. This gives the rcu_read_lock() 79 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other 80 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. 81 */ 82 #define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting) 83 84 #else /* #ifdef CONFIG_PREEMPT_RCU */ 85 86 #ifdef CONFIG_TINY_RCU 87 #define rcu_read_unlock_strict() do { } while (0) 88 #else 89 void rcu_read_unlock_strict(void); 90 #endif 91 92 static inline void __rcu_read_lock(void) 93 { 94 preempt_disable(); 95 } 96 97 static inline void __rcu_read_unlock(void) 98 { 99 preempt_enable(); 100 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) 101 rcu_read_unlock_strict(); 102 } 103 104 static inline int rcu_preempt_depth(void) 105 { 106 return 0; 107 } 108 109 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 110 111 /* Internal to kernel */ 112 void rcu_init(void); 113 extern int rcu_scheduler_active; 114 void rcu_sched_clock_irq(int user); 115 void rcu_report_dead(unsigned int cpu); 116 void rcutree_migrate_callbacks(int cpu); 117 118 #ifdef CONFIG_TASKS_RCU_GENERIC 119 void rcu_init_tasks_generic(void); 120 #else 121 static inline void rcu_init_tasks_generic(void) { } 122 #endif 123 124 #ifdef CONFIG_RCU_STALL_COMMON 125 void rcu_sysrq_start(void); 126 void rcu_sysrq_end(void); 127 #else /* #ifdef CONFIG_RCU_STALL_COMMON */ 128 static inline void rcu_sysrq_start(void) { } 129 static inline void rcu_sysrq_end(void) { } 130 #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */ 131 132 #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) 133 void rcu_irq_work_resched(void); 134 #else 135 static inline void rcu_irq_work_resched(void) { } 136 #endif 137 138 #ifdef CONFIG_RCU_NOCB_CPU 139 void rcu_init_nohz(void); 140 int rcu_nocb_cpu_offload(int cpu); 141 int rcu_nocb_cpu_deoffload(int cpu); 142 void rcu_nocb_flush_deferred_wakeup(void); 143 #else /* #ifdef CONFIG_RCU_NOCB_CPU */ 144 static inline void rcu_init_nohz(void) { } 145 static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; } 146 static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; } 147 static inline void rcu_nocb_flush_deferred_wakeup(void) { } 148 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ 149 150 /** 151 * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers 152 * @a: Code that RCU needs to pay attention to. 153 * 154 * RCU read-side critical sections are forbidden in the inner idle loop, 155 * that is, between the ct_idle_enter() and the ct_idle_exit() -- RCU 156 * will happily ignore any such read-side critical sections. However, 157 * things like powertop need tracepoints in the inner idle loop. 158 * 159 * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) 160 * will tell RCU that it needs to pay attention, invoke its argument 161 * (in this example, calling the do_something_with_RCU() function), 162 * and then tell RCU to go back to ignoring this CPU. It is permissible 163 * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is 164 * on the order of a million or so, even on 32-bit systems). It is 165 * not legal to block within RCU_NONIDLE(), nor is it permissible to 166 * transfer control either into or out of RCU_NONIDLE()'s statement. 167 */ 168 #define RCU_NONIDLE(a) \ 169 do { \ 170 ct_irq_enter_irqson(); \ 171 do { a; } while (0); \ 172 ct_irq_exit_irqson(); \ 173 } while (0) 174 175 /* 176 * Note a quasi-voluntary context switch for RCU-tasks's benefit. 177 * This is a macro rather than an inline function to avoid #include hell. 178 */ 179 #ifdef CONFIG_TASKS_RCU_GENERIC 180 181 # ifdef CONFIG_TASKS_RCU 182 # define rcu_tasks_classic_qs(t, preempt) \ 183 do { \ 184 if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \ 185 WRITE_ONCE((t)->rcu_tasks_holdout, false); \ 186 } while (0) 187 void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); 188 void synchronize_rcu_tasks(void); 189 # else 190 # define rcu_tasks_classic_qs(t, preempt) do { } while (0) 191 # define call_rcu_tasks call_rcu 192 # define synchronize_rcu_tasks synchronize_rcu 193 # endif 194 195 # ifdef CONFIG_TASKS_TRACE_RCU 196 // Bits for ->trc_reader_special.b.need_qs field. 197 #define TRC_NEED_QS 0x1 // Task needs a quiescent state. 198 #define TRC_NEED_QS_CHECKED 0x2 // Task has been checked for needing quiescent state. 199 200 u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new); 201 void rcu_tasks_trace_qs_blkd(struct task_struct *t); 202 203 # define rcu_tasks_trace_qs(t) \ 204 do { \ 205 int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting); \ 206 \ 207 if (likely(!READ_ONCE((t)->trc_reader_special.b.need_qs)) && \ 208 likely(!___rttq_nesting)) { \ 209 rcu_trc_cmpxchg_need_qs((t), 0, TRC_NEED_QS_CHECKED); \ 210 } else if (___rttq_nesting && ___rttq_nesting != INT_MIN && \ 211 !READ_ONCE((t)->trc_reader_special.b.blocked)) { \ 212 rcu_tasks_trace_qs_blkd(t); \ 213 } \ 214 } while (0) 215 # else 216 # define rcu_tasks_trace_qs(t) do { } while (0) 217 # endif 218 219 #define rcu_tasks_qs(t, preempt) \ 220 do { \ 221 rcu_tasks_classic_qs((t), (preempt)); \ 222 rcu_tasks_trace_qs(t); \ 223 } while (0) 224 225 # ifdef CONFIG_TASKS_RUDE_RCU 226 void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func); 227 void synchronize_rcu_tasks_rude(void); 228 # endif 229 230 #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false) 231 void exit_tasks_rcu_start(void); 232 void exit_tasks_rcu_finish(void); 233 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ 234 #define rcu_tasks_classic_qs(t, preempt) do { } while (0) 235 #define rcu_tasks_qs(t, preempt) do { } while (0) 236 #define rcu_note_voluntary_context_switch(t) do { } while (0) 237 #define call_rcu_tasks call_rcu 238 #define synchronize_rcu_tasks synchronize_rcu 239 static inline void exit_tasks_rcu_start(void) { } 240 static inline void exit_tasks_rcu_finish(void) { } 241 #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ 242 243 /** 244 * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an RCU grace period? 245 * 246 * As an accident of implementation, an RCU Tasks Trace grace period also 247 * acts as an RCU grace period. However, this could change at any time. 248 * Code relying on this accident must call this function to verify that 249 * this accident is still happening. 250 * 251 * You have been warned! 252 */ 253 static inline bool rcu_trace_implies_rcu_gp(void) { return true; } 254 255 /** 256 * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU 257 * 258 * This macro resembles cond_resched(), except that it is defined to 259 * report potential quiescent states to RCU-tasks even if the cond_resched() 260 * machinery were to be shut off, as some advocate for PREEMPTION kernels. 261 */ 262 #define cond_resched_tasks_rcu_qs() \ 263 do { \ 264 rcu_tasks_qs(current, false); \ 265 cond_resched(); \ 266 } while (0) 267 268 /* 269 * Infrastructure to implement the synchronize_() primitives in 270 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. 271 */ 272 273 #if defined(CONFIG_TREE_RCU) 274 #include <linux/rcutree.h> 275 #elif defined(CONFIG_TINY_RCU) 276 #include <linux/rcutiny.h> 277 #else 278 #error "Unknown RCU implementation specified to kernel configuration" 279 #endif 280 281 /* 282 * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls 283 * are needed for dynamic initialization and destruction of rcu_head 284 * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for 285 * dynamic initialization and destruction of statically allocated rcu_head 286 * structures. However, rcu_head structures allocated dynamically in the 287 * heap don't need any initialization. 288 */ 289 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 290 void init_rcu_head(struct rcu_head *head); 291 void destroy_rcu_head(struct rcu_head *head); 292 void init_rcu_head_on_stack(struct rcu_head *head); 293 void destroy_rcu_head_on_stack(struct rcu_head *head); 294 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 295 static inline void init_rcu_head(struct rcu_head *head) { } 296 static inline void destroy_rcu_head(struct rcu_head *head) { } 297 static inline void init_rcu_head_on_stack(struct rcu_head *head) { } 298 static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { } 299 #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 300 301 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) 302 bool rcu_lockdep_current_cpu_online(void); 303 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ 304 static inline bool rcu_lockdep_current_cpu_online(void) { return true; } 305 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ 306 307 extern struct lockdep_map rcu_lock_map; 308 extern struct lockdep_map rcu_bh_lock_map; 309 extern struct lockdep_map rcu_sched_lock_map; 310 extern struct lockdep_map rcu_callback_map; 311 312 #ifdef CONFIG_DEBUG_LOCK_ALLOC 313 314 static inline void rcu_lock_acquire(struct lockdep_map *map) 315 { 316 lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_); 317 } 318 319 static inline void rcu_lock_release(struct lockdep_map *map) 320 { 321 lock_release(map, _THIS_IP_); 322 } 323 324 int debug_lockdep_rcu_enabled(void); 325 int rcu_read_lock_held(void); 326 int rcu_read_lock_bh_held(void); 327 int rcu_read_lock_sched_held(void); 328 int rcu_read_lock_any_held(void); 329 330 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 331 332 # define rcu_lock_acquire(a) do { } while (0) 333 # define rcu_lock_release(a) do { } while (0) 334 335 static inline int rcu_read_lock_held(void) 336 { 337 return 1; 338 } 339 340 static inline int rcu_read_lock_bh_held(void) 341 { 342 return 1; 343 } 344 345 static inline int rcu_read_lock_sched_held(void) 346 { 347 return !preemptible(); 348 } 349 350 static inline int rcu_read_lock_any_held(void) 351 { 352 return !preemptible(); 353 } 354 355 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 356 357 #ifdef CONFIG_PROVE_RCU 358 359 /** 360 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met 361 * @c: condition to check 362 * @s: informative message 363 */ 364 #define RCU_LOCKDEP_WARN(c, s) \ 365 do { \ 366 static bool __section(".data.unlikely") __warned; \ 367 if ((c) && debug_lockdep_rcu_enabled() && !__warned) { \ 368 __warned = true; \ 369 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ 370 } \ 371 } while (0) 372 373 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU) 374 static inline void rcu_preempt_sleep_check(void) 375 { 376 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map), 377 "Illegal context switch in RCU read-side critical section"); 378 } 379 #else /* #ifdef CONFIG_PROVE_RCU */ 380 static inline void rcu_preempt_sleep_check(void) { } 381 #endif /* #else #ifdef CONFIG_PROVE_RCU */ 382 383 #define rcu_sleep_check() \ 384 do { \ 385 rcu_preempt_sleep_check(); \ 386 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \ 387 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \ 388 "Illegal context switch in RCU-bh read-side critical section"); \ 389 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \ 390 "Illegal context switch in RCU-sched read-side critical section"); \ 391 } while (0) 392 393 #else /* #ifdef CONFIG_PROVE_RCU */ 394 395 #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c)) 396 #define rcu_sleep_check() do { } while (0) 397 398 #endif /* #else #ifdef CONFIG_PROVE_RCU */ 399 400 /* 401 * Helper functions for rcu_dereference_check(), rcu_dereference_protected() 402 * and rcu_assign_pointer(). Some of these could be folded into their 403 * callers, but they are left separate in order to ease introduction of 404 * multiple pointers markings to match different RCU implementations 405 * (e.g., __srcu), should this make sense in the future. 406 */ 407 408 #ifdef __CHECKER__ 409 #define rcu_check_sparse(p, space) \ 410 ((void)(((typeof(*p) space *)p) == p)) 411 #else /* #ifdef __CHECKER__ */ 412 #define rcu_check_sparse(p, space) 413 #endif /* #else #ifdef __CHECKER__ */ 414 415 #define __unrcu_pointer(p, local) \ 416 ({ \ 417 typeof(*p) *local = (typeof(*p) *__force)(p); \ 418 rcu_check_sparse(p, __rcu); \ 419 ((typeof(*p) __force __kernel *)(local)); \ 420 }) 421 /** 422 * unrcu_pointer - mark a pointer as not being RCU protected 423 * @p: pointer needing to lose its __rcu property 424 * 425 * Converts @p from an __rcu pointer to a __kernel pointer. 426 * This allows an __rcu pointer to be used with xchg() and friends. 427 */ 428 #define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu)) 429 430 #define __rcu_access_pointer(p, local, space) \ 431 ({ \ 432 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ 433 rcu_check_sparse(p, space); \ 434 ((typeof(*p) __force __kernel *)(local)); \ 435 }) 436 #define __rcu_dereference_check(p, local, c, space) \ 437 ({ \ 438 /* Dependency order vs. p above. */ \ 439 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ 440 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ 441 rcu_check_sparse(p, space); \ 442 ((typeof(*p) __force __kernel *)(local)); \ 443 }) 444 #define __rcu_dereference_protected(p, local, c, space) \ 445 ({ \ 446 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ 447 rcu_check_sparse(p, space); \ 448 ((typeof(*p) __force __kernel *)(p)); \ 449 }) 450 #define __rcu_dereference_raw(p, local) \ 451 ({ \ 452 /* Dependency order vs. p above. */ \ 453 typeof(p) local = READ_ONCE(p); \ 454 ((typeof(*p) __force __kernel *)(local)); \ 455 }) 456 #define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu)) 457 458 /** 459 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable 460 * @v: The value to statically initialize with. 461 */ 462 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) 463 464 /** 465 * rcu_assign_pointer() - assign to RCU-protected pointer 466 * @p: pointer to assign to 467 * @v: value to assign (publish) 468 * 469 * Assigns the specified value to the specified RCU-protected 470 * pointer, ensuring that any concurrent RCU readers will see 471 * any prior initialization. 472 * 473 * Inserts memory barriers on architectures that require them 474 * (which is most of them), and also prevents the compiler from 475 * reordering the code that initializes the structure after the pointer 476 * assignment. More importantly, this call documents which pointers 477 * will be dereferenced by RCU read-side code. 478 * 479 * In some special cases, you may use RCU_INIT_POINTER() instead 480 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due 481 * to the fact that it does not constrain either the CPU or the compiler. 482 * That said, using RCU_INIT_POINTER() when you should have used 483 * rcu_assign_pointer() is a very bad thing that results in 484 * impossible-to-diagnose memory corruption. So please be careful. 485 * See the RCU_INIT_POINTER() comment header for details. 486 * 487 * Note that rcu_assign_pointer() evaluates each of its arguments only 488 * once, appearances notwithstanding. One of the "extra" evaluations 489 * is in typeof() and the other visible only to sparse (__CHECKER__), 490 * neither of which actually execute the argument. As with most cpp 491 * macros, this execute-arguments-only-once property is important, so 492 * please be careful when making changes to rcu_assign_pointer() and the 493 * other macros that it invokes. 494 */ 495 #define rcu_assign_pointer(p, v) \ 496 do { \ 497 uintptr_t _r_a_p__v = (uintptr_t)(v); \ 498 rcu_check_sparse(p, __rcu); \ 499 \ 500 if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \ 501 WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \ 502 else \ 503 smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ 504 } while (0) 505 506 /** 507 * rcu_replace_pointer() - replace an RCU pointer, returning its old value 508 * @rcu_ptr: RCU pointer, whose old value is returned 509 * @ptr: regular pointer 510 * @c: the lockdep conditions under which the dereference will take place 511 * 512 * Perform a replacement, where @rcu_ptr is an RCU-annotated 513 * pointer and @c is the lockdep argument that is passed to the 514 * rcu_dereference_protected() call used to read that pointer. The old 515 * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr. 516 */ 517 #define rcu_replace_pointer(rcu_ptr, ptr, c) \ 518 ({ \ 519 typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ 520 rcu_assign_pointer((rcu_ptr), (ptr)); \ 521 __tmp; \ 522 }) 523 524 /** 525 * rcu_access_pointer() - fetch RCU pointer with no dereferencing 526 * @p: The pointer to read 527 * 528 * Return the value of the specified RCU-protected pointer, but omit the 529 * lockdep checks for being in an RCU read-side critical section. This is 530 * useful when the value of this pointer is accessed, but the pointer is 531 * not dereferenced, for example, when testing an RCU-protected pointer 532 * against NULL. Although rcu_access_pointer() may also be used in cases 533 * where update-side locks prevent the value of the pointer from changing, 534 * you should instead use rcu_dereference_protected() for this use case. 535 * Within an RCU read-side critical section, there is little reason to 536 * use rcu_access_pointer(). 537 * 538 * It is usually best to test the rcu_access_pointer() return value 539 * directly in order to avoid accidental dereferences being introduced 540 * by later inattentive changes. In other words, assigning the 541 * rcu_access_pointer() return value to a local variable results in an 542 * accident waiting to happen. 543 * 544 * It is also permissible to use rcu_access_pointer() when read-side 545 * access to the pointer was removed at least one grace period ago, as is 546 * the case in the context of the RCU callback that is freeing up the data, 547 * or after a synchronize_rcu() returns. This can be useful when tearing 548 * down multi-linked structures after a grace period has elapsed. However, 549 * rcu_dereference_protected() is normally preferred for this use case. 550 */ 551 #define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu) 552 553 /** 554 * rcu_dereference_check() - rcu_dereference with debug checking 555 * @p: The pointer to read, prior to dereferencing 556 * @c: The conditions under which the dereference will take place 557 * 558 * Do an rcu_dereference(), but check that the conditions under which the 559 * dereference will take place are correct. Typically the conditions 560 * indicate the various locking conditions that should be held at that 561 * point. The check should return true if the conditions are satisfied. 562 * An implicit check for being in an RCU read-side critical section 563 * (rcu_read_lock()) is included. 564 * 565 * For example: 566 * 567 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); 568 * 569 * could be used to indicate to lockdep that foo->bar may only be dereferenced 570 * if either rcu_read_lock() is held, or that the lock required to replace 571 * the bar struct at foo->bar is held. 572 * 573 * Note that the list of conditions may also include indications of when a lock 574 * need not be held, for example during initialisation or destruction of the 575 * target struct: 576 * 577 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || 578 * atomic_read(&foo->usage) == 0); 579 * 580 * Inserts memory barriers on architectures that require them 581 * (currently only the Alpha), prevents the compiler from refetching 582 * (and from merging fetches), and, more importantly, documents exactly 583 * which pointers are protected by RCU and checks that the pointer is 584 * annotated as __rcu. 585 */ 586 #define rcu_dereference_check(p, c) \ 587 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 588 (c) || rcu_read_lock_held(), __rcu) 589 590 /** 591 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking 592 * @p: The pointer to read, prior to dereferencing 593 * @c: The conditions under which the dereference will take place 594 * 595 * This is the RCU-bh counterpart to rcu_dereference_check(). However, 596 * please note that starting in v5.0 kernels, vanilla RCU grace periods 597 * wait for local_bh_disable() regions of code in addition to regions of 598 * code demarked by rcu_read_lock() and rcu_read_unlock(). This means 599 * that synchronize_rcu(), call_rcu, and friends all take not only 600 * rcu_read_lock() but also rcu_read_lock_bh() into account. 601 */ 602 #define rcu_dereference_bh_check(p, c) \ 603 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 604 (c) || rcu_read_lock_bh_held(), __rcu) 605 606 /** 607 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking 608 * @p: The pointer to read, prior to dereferencing 609 * @c: The conditions under which the dereference will take place 610 * 611 * This is the RCU-sched counterpart to rcu_dereference_check(). 612 * However, please note that starting in v5.0 kernels, vanilla RCU grace 613 * periods wait for preempt_disable() regions of code in addition to 614 * regions of code demarked by rcu_read_lock() and rcu_read_unlock(). 615 * This means that synchronize_rcu(), call_rcu, and friends all take not 616 * only rcu_read_lock() but also rcu_read_lock_sched() into account. 617 */ 618 #define rcu_dereference_sched_check(p, c) \ 619 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 620 (c) || rcu_read_lock_sched_held(), \ 621 __rcu) 622 623 /* 624 * The tracing infrastructure traces RCU (we want that), but unfortunately 625 * some of the RCU checks causes tracing to lock up the system. 626 * 627 * The no-tracing version of rcu_dereference_raw() must not call 628 * rcu_read_lock_held(). 629 */ 630 #define rcu_dereference_raw_check(p) \ 631 __rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu) 632 633 /** 634 * rcu_dereference_protected() - fetch RCU pointer when updates prevented 635 * @p: The pointer to read, prior to dereferencing 636 * @c: The conditions under which the dereference will take place 637 * 638 * Return the value of the specified RCU-protected pointer, but omit 639 * the READ_ONCE(). This is useful in cases where update-side locks 640 * prevent the value of the pointer from changing. Please note that this 641 * primitive does *not* prevent the compiler from repeating this reference 642 * or combining it with other references, so it should not be used without 643 * protection of appropriate locks. 644 * 645 * This function is only for update-side use. Using this function 646 * when protected only by rcu_read_lock() will result in infrequent 647 * but very ugly failures. 648 */ 649 #define rcu_dereference_protected(p, c) \ 650 __rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu) 651 652 653 /** 654 * rcu_dereference() - fetch RCU-protected pointer for dereferencing 655 * @p: The pointer to read, prior to dereferencing 656 * 657 * This is a simple wrapper around rcu_dereference_check(). 658 */ 659 #define rcu_dereference(p) rcu_dereference_check(p, 0) 660 661 /** 662 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing 663 * @p: The pointer to read, prior to dereferencing 664 * 665 * Makes rcu_dereference_check() do the dirty work. 666 */ 667 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) 668 669 /** 670 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing 671 * @p: The pointer to read, prior to dereferencing 672 * 673 * Makes rcu_dereference_check() do the dirty work. 674 */ 675 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) 676 677 /** 678 * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism 679 * @p: The pointer to hand off 680 * 681 * This is simply an identity function, but it documents where a pointer 682 * is handed off from RCU to some other synchronization mechanism, for 683 * example, reference counting or locking. In C11, it would map to 684 * kill_dependency(). It could be used as follows:: 685 * 686 * rcu_read_lock(); 687 * p = rcu_dereference(gp); 688 * long_lived = is_long_lived(p); 689 * if (long_lived) { 690 * if (!atomic_inc_not_zero(p->refcnt)) 691 * long_lived = false; 692 * else 693 * p = rcu_pointer_handoff(p); 694 * } 695 * rcu_read_unlock(); 696 */ 697 #define rcu_pointer_handoff(p) (p) 698 699 /** 700 * rcu_read_lock() - mark the beginning of an RCU read-side critical section 701 * 702 * When synchronize_rcu() is invoked on one CPU while other CPUs 703 * are within RCU read-side critical sections, then the 704 * synchronize_rcu() is guaranteed to block until after all the other 705 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked 706 * on one CPU while other CPUs are within RCU read-side critical 707 * sections, invocation of the corresponding RCU callback is deferred 708 * until after the all the other CPUs exit their critical sections. 709 * 710 * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also 711 * wait for regions of code with preemption disabled, including regions of 712 * code with interrupts or softirqs disabled. In pre-v5.0 kernels, which 713 * define synchronize_sched(), only code enclosed within rcu_read_lock() 714 * and rcu_read_unlock() are guaranteed to be waited for. 715 * 716 * Note, however, that RCU callbacks are permitted to run concurrently 717 * with new RCU read-side critical sections. One way that this can happen 718 * is via the following sequence of events: (1) CPU 0 enters an RCU 719 * read-side critical section, (2) CPU 1 invokes call_rcu() to register 720 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, 721 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU 722 * callback is invoked. This is legal, because the RCU read-side critical 723 * section that was running concurrently with the call_rcu() (and which 724 * therefore might be referencing something that the corresponding RCU 725 * callback would free up) has completed before the corresponding 726 * RCU callback is invoked. 727 * 728 * RCU read-side critical sections may be nested. Any deferred actions 729 * will be deferred until the outermost RCU read-side critical section 730 * completes. 731 * 732 * You can avoid reading and understanding the next paragraph by 733 * following this rule: don't put anything in an rcu_read_lock() RCU 734 * read-side critical section that would block in a !PREEMPTION kernel. 735 * But if you want the full story, read on! 736 * 737 * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU), 738 * it is illegal to block while in an RCU read-side critical section. 739 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION 740 * kernel builds, RCU read-side critical sections may be preempted, 741 * but explicit blocking is illegal. Finally, in preemptible RCU 742 * implementations in real-time (with -rt patchset) kernel builds, RCU 743 * read-side critical sections may be preempted and they may also block, but 744 * only when acquiring spinlocks that are subject to priority inheritance. 745 */ 746 static __always_inline void rcu_read_lock(void) 747 { 748 __rcu_read_lock(); 749 __acquire(RCU); 750 rcu_lock_acquire(&rcu_lock_map); 751 RCU_LOCKDEP_WARN(!rcu_is_watching(), 752 "rcu_read_lock() used illegally while idle"); 753 } 754 755 /* 756 * So where is rcu_write_lock()? It does not exist, as there is no 757 * way for writers to lock out RCU readers. This is a feature, not 758 * a bug -- this property is what provides RCU's performance benefits. 759 * Of course, writers must coordinate with each other. The normal 760 * spinlock primitives work well for this, but any other technique may be 761 * used as well. RCU does not care how the writers keep out of each 762 * others' way, as long as they do so. 763 */ 764 765 /** 766 * rcu_read_unlock() - marks the end of an RCU read-side critical section. 767 * 768 * In almost all situations, rcu_read_unlock() is immune from deadlock. 769 * In recent kernels that have consolidated synchronize_sched() and 770 * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity 771 * also extends to the scheduler's runqueue and priority-inheritance 772 * spinlocks, courtesy of the quiescent-state deferral that is carried 773 * out when rcu_read_unlock() is invoked with interrupts disabled. 774 * 775 * See rcu_read_lock() for more information. 776 */ 777 static inline void rcu_read_unlock(void) 778 { 779 RCU_LOCKDEP_WARN(!rcu_is_watching(), 780 "rcu_read_unlock() used illegally while idle"); 781 __release(RCU); 782 __rcu_read_unlock(); 783 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ 784 } 785 786 /** 787 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section 788 * 789 * This is equivalent to rcu_read_lock(), but also disables softirqs. 790 * Note that anything else that disables softirqs can also serve as an RCU 791 * read-side critical section. However, please note that this equivalence 792 * applies only to v5.0 and later. Before v5.0, rcu_read_lock() and 793 * rcu_read_lock_bh() were unrelated. 794 * 795 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() 796 * must occur in the same context, for example, it is illegal to invoke 797 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() 798 * was invoked from some other task. 799 */ 800 static inline void rcu_read_lock_bh(void) 801 { 802 local_bh_disable(); 803 __acquire(RCU_BH); 804 rcu_lock_acquire(&rcu_bh_lock_map); 805 RCU_LOCKDEP_WARN(!rcu_is_watching(), 806 "rcu_read_lock_bh() used illegally while idle"); 807 } 808 809 /** 810 * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section 811 * 812 * See rcu_read_lock_bh() for more information. 813 */ 814 static inline void rcu_read_unlock_bh(void) 815 { 816 RCU_LOCKDEP_WARN(!rcu_is_watching(), 817 "rcu_read_unlock_bh() used illegally while idle"); 818 rcu_lock_release(&rcu_bh_lock_map); 819 __release(RCU_BH); 820 local_bh_enable(); 821 } 822 823 /** 824 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section 825 * 826 * This is equivalent to rcu_read_lock(), but also disables preemption. 827 * Read-side critical sections can also be introduced by anything else that 828 * disables preemption, including local_irq_disable() and friends. However, 829 * please note that the equivalence to rcu_read_lock() applies only to 830 * v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched() 831 * were unrelated. 832 * 833 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() 834 * must occur in the same context, for example, it is illegal to invoke 835 * rcu_read_unlock_sched() from process context if the matching 836 * rcu_read_lock_sched() was invoked from an NMI handler. 837 */ 838 static inline void rcu_read_lock_sched(void) 839 { 840 preempt_disable(); 841 __acquire(RCU_SCHED); 842 rcu_lock_acquire(&rcu_sched_lock_map); 843 RCU_LOCKDEP_WARN(!rcu_is_watching(), 844 "rcu_read_lock_sched() used illegally while idle"); 845 } 846 847 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 848 static inline notrace void rcu_read_lock_sched_notrace(void) 849 { 850 preempt_disable_notrace(); 851 __acquire(RCU_SCHED); 852 } 853 854 /** 855 * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section 856 * 857 * See rcu_read_lock_sched() for more information. 858 */ 859 static inline void rcu_read_unlock_sched(void) 860 { 861 RCU_LOCKDEP_WARN(!rcu_is_watching(), 862 "rcu_read_unlock_sched() used illegally while idle"); 863 rcu_lock_release(&rcu_sched_lock_map); 864 __release(RCU_SCHED); 865 preempt_enable(); 866 } 867 868 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 869 static inline notrace void rcu_read_unlock_sched_notrace(void) 870 { 871 __release(RCU_SCHED); 872 preempt_enable_notrace(); 873 } 874 875 /** 876 * RCU_INIT_POINTER() - initialize an RCU protected pointer 877 * @p: The pointer to be initialized. 878 * @v: The value to initialized the pointer to. 879 * 880 * Initialize an RCU-protected pointer in special cases where readers 881 * do not need ordering constraints on the CPU or the compiler. These 882 * special cases are: 883 * 884 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or* 885 * 2. The caller has taken whatever steps are required to prevent 886 * RCU readers from concurrently accessing this pointer *or* 887 * 3. The referenced data structure has already been exposed to 888 * readers either at compile time or via rcu_assign_pointer() *and* 889 * 890 * a. You have not made *any* reader-visible changes to 891 * this structure since then *or* 892 * b. It is OK for readers accessing this structure from its 893 * new location to see the old state of the structure. (For 894 * example, the changes were to statistical counters or to 895 * other state where exact synchronization is not required.) 896 * 897 * Failure to follow these rules governing use of RCU_INIT_POINTER() will 898 * result in impossible-to-diagnose memory corruption. As in the structures 899 * will look OK in crash dumps, but any concurrent RCU readers might 900 * see pre-initialized values of the referenced data structure. So 901 * please be very careful how you use RCU_INIT_POINTER()!!! 902 * 903 * If you are creating an RCU-protected linked structure that is accessed 904 * by a single external-to-structure RCU-protected pointer, then you may 905 * use RCU_INIT_POINTER() to initialize the internal RCU-protected 906 * pointers, but you must use rcu_assign_pointer() to initialize the 907 * external-to-structure pointer *after* you have completely initialized 908 * the reader-accessible portions of the linked structure. 909 * 910 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no 911 * ordering guarantees for either the CPU or the compiler. 912 */ 913 #define RCU_INIT_POINTER(p, v) \ 914 do { \ 915 rcu_check_sparse(p, __rcu); \ 916 WRITE_ONCE(p, RCU_INITIALIZER(v)); \ 917 } while (0) 918 919 /** 920 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer 921 * @p: The pointer to be initialized. 922 * @v: The value to initialized the pointer to. 923 * 924 * GCC-style initialization for an RCU-protected pointer in a structure field. 925 */ 926 #define RCU_POINTER_INITIALIZER(p, v) \ 927 .p = RCU_INITIALIZER(v) 928 929 /* 930 * Does the specified offset indicate that the corresponding rcu_head 931 * structure can be handled by kvfree_rcu()? 932 */ 933 #define __is_kvfree_rcu_offset(offset) ((offset) < 4096) 934 935 /** 936 * kfree_rcu() - kfree an object after a grace period. 937 * @ptr: pointer to kfree for both single- and double-argument invocations. 938 * @rhf: the name of the struct rcu_head within the type of @ptr, 939 * but only for double-argument invocations. 940 * 941 * Many rcu callbacks functions just call kfree() on the base structure. 942 * These functions are trivial, but their size adds up, and furthermore 943 * when they are used in a kernel module, that module must invoke the 944 * high-latency rcu_barrier() function at module-unload time. 945 * 946 * The kfree_rcu() function handles this issue. Rather than encoding a 947 * function address in the embedded rcu_head structure, kfree_rcu() instead 948 * encodes the offset of the rcu_head structure within the base structure. 949 * Because the functions are not allowed in the low-order 4096 bytes of 950 * kernel virtual memory, offsets up to 4095 bytes can be accommodated. 951 * If the offset is larger than 4095 bytes, a compile-time error will 952 * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can 953 * either fall back to use of call_rcu() or rearrange the structure to 954 * position the rcu_head structure into the first 4096 bytes. 955 * 956 * Note that the allowable offset might decrease in the future, for example, 957 * to allow something like kmem_cache_free_rcu(). 958 * 959 * The BUILD_BUG_ON check must not involve any function calls, hence the 960 * checks are done in macros here. 961 */ 962 #define kfree_rcu(ptr, rhf...) kvfree_rcu(ptr, ## rhf) 963 964 /** 965 * kvfree_rcu() - kvfree an object after a grace period. 966 * 967 * This macro consists of one or two arguments and it is 968 * based on whether an object is head-less or not. If it 969 * has a head then a semantic stays the same as it used 970 * to be before: 971 * 972 * kvfree_rcu(ptr, rhf); 973 * 974 * where @ptr is a pointer to kvfree(), @rhf is the name 975 * of the rcu_head structure within the type of @ptr. 976 * 977 * When it comes to head-less variant, only one argument 978 * is passed and that is just a pointer which has to be 979 * freed after a grace period. Therefore the semantic is 980 * 981 * kvfree_rcu(ptr); 982 * 983 * where @ptr is the pointer to be freed by kvfree(). 984 * 985 * Please note, head-less way of freeing is permitted to 986 * use from a context that has to follow might_sleep() 987 * annotation. Otherwise, please switch and embed the 988 * rcu_head structure within the type of @ptr. 989 */ 990 #define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__, \ 991 kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__) 992 993 #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME 994 #define kvfree_rcu_arg_2(ptr, rhf) \ 995 do { \ 996 typeof (ptr) ___p = (ptr); \ 997 \ 998 if (___p) { \ 999 BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf))); \ 1000 kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long) \ 1001 (offsetof(typeof(*(ptr)), rhf))); \ 1002 } \ 1003 } while (0) 1004 1005 #define kvfree_rcu_arg_1(ptr) \ 1006 do { \ 1007 typeof(ptr) ___p = (ptr); \ 1008 \ 1009 if (___p) \ 1010 kvfree_call_rcu(NULL, (rcu_callback_t) (___p)); \ 1011 } while (0) 1012 1013 /* 1014 * Place this after a lock-acquisition primitive to guarantee that 1015 * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies 1016 * if the UNLOCK and LOCK are executed by the same CPU or if the 1017 * UNLOCK and LOCK operate on the same lock variable. 1018 */ 1019 #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE 1020 #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ 1021 #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ 1022 #define smp_mb__after_unlock_lock() do { } while (0) 1023 #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ 1024 1025 1026 /* Has the specified rcu_head structure been handed to call_rcu()? */ 1027 1028 /** 1029 * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu() 1030 * @rhp: The rcu_head structure to initialize. 1031 * 1032 * If you intend to invoke rcu_head_after_call_rcu() to test whether a 1033 * given rcu_head structure has already been passed to call_rcu(), then 1034 * you must also invoke this rcu_head_init() function on it just after 1035 * allocating that structure. Calls to this function must not race with 1036 * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation. 1037 */ 1038 static inline void rcu_head_init(struct rcu_head *rhp) 1039 { 1040 rhp->func = (rcu_callback_t)~0L; 1041 } 1042 1043 /** 1044 * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()? 1045 * @rhp: The rcu_head structure to test. 1046 * @f: The function passed to call_rcu() along with @rhp. 1047 * 1048 * Returns @true if the @rhp has been passed to call_rcu() with @func, 1049 * and @false otherwise. Emits a warning in any other case, including 1050 * the case where @rhp has already been invoked after a grace period. 1051 * Calls to this function must not race with callback invocation. One way 1052 * to avoid such races is to enclose the call to rcu_head_after_call_rcu() 1053 * in an RCU read-side critical section that includes a read-side fetch 1054 * of the pointer to the structure containing @rhp. 1055 */ 1056 static inline bool 1057 rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) 1058 { 1059 rcu_callback_t func = READ_ONCE(rhp->func); 1060 1061 if (func == f) 1062 return true; 1063 WARN_ON_ONCE(func != (rcu_callback_t)~0L); 1064 return false; 1065 } 1066 1067 /* kernel/ksysfs.c definitions */ 1068 extern int rcu_expedited; 1069 extern int rcu_normal; 1070 1071 #endif /* __LINUX_RCUPDATE_H */ 1072